This invention relates to flow controllers for combustion engines and more particularly, though not exclusively, to a ducted rotary inlet flow controller designed and adapted to aerodynamically control the airflow quantity and velocity at the inlet to a pulse detonation engine (PDE).
In the prior art, turbojet and turbofan engines have been directly attached to aircraft inlets without an interface being required. These engines require constant and near-uniform airflow supply, and include compressors and turbines that are complex and expensive. They are generally limited to flight speeds less than Mach 3 because of high temperatures. The current demand is for more fuel efficient, simpler, and lighter weight engine systems. Predicted performance for pulse detonation engines indicates that these engines offer increased efficiency over current systems, and that this increased efficiency is available over a wide range of flight speeds. The PDE offers several additional advantages over a conventional turbomachinery based engine system. These engines offer simplicity and light weight. The PDE is scalable over a range of sizes, and very small engines are possible. They also offer geometric flexibility that allows a wider range of more efficient propulsion/airframe integration schemes. However, the pulse detonation engine imposes different airflow demands on the high-speed inlet than a conventional turbojet engines. The PDE airflow demand is in a cyclic xe2x80x9con/off xe2x80x9d manner. Combustion chambers of a pulse detonation engine are similar to the pistons of an automobile gasoline engine. Airflow and fuel are injected into the chamber to form a combustible mixture with a detonation initiated by a spark source. In the case of a pulse detonation engine, the explosion of the air and fuel mixture creates a high-pressure wave that moves down the combustion tube to the exit. The large increase in pressure in the chamber from the detonation of the combustible mixture results in propulsive thrust. The cycle for each combustion chamber of the pulse detonation engine is airflow fill (airflow entrance open) and fuel injection, airflow entrance closed, ignition, high combustion chamber pressure, and exhaust from the open end of the combustion chamber. At the beginning of the propulsive cycle, the combustion chamber is opened to the inlet airflow supply. Fuel is injected with the airflow to enhance mixing. The chamber is then sealed to the incoming airflow, thus eliminating the demand of airflow from the inlet. The combustible mixture is ignited and the high pressure created by the detonation provides a thrust force on the forward wall of the chamber. The chamber then is re-opened to draw additional airflow for the next combustion cycle. A high-speed valve must provide this opening and closing of the airflow supply port. A high-speed valve is required since high engine efficiency typically requires combustion frequencies of as much as (or more than) 100 Hertz. Multiple pulse detonation combustion chambers can be located at the diffuser exit of a high-speed inlet and fired alternately. However, if a conventional design for an airflow control valve, such as the valve disclosed in U.S. Pat. No. 5,901,550 to Bussing et al is used, less than 50% of the inlet diffuser exit area is available for airflow into the engine. Less than half of the diffuser exit area is available because some overlap is required for sealing of the chamber from the incoming air supply duct and to allow for proper combustion. Typically, multiples of two chambers would be used. If two large chambers are used (one open and one closed), then the engine would demand only a part of the available airflow at the exit. If four valves are used, then two would open as two were closed, providing the same demand if only two larger chambers are used. As the valve moves to close one chamber and open the next chamber, the airflow demand decreases and then increases as the next chamber is filled. This cyclic demand for airflow places severe requirements on the inlet.
The innovative design disclosed herein provides a rotary inlet flow controller, with one or more open ducts extending through the controller. The ducts are designed and adapted to aerodynamically control the amount and velocity of the flow of air to combustion chambers of a pulse detonation engine without imposing large cyclic airflow transients in the diffuser of the air intake. The ducted rotary inlet flow controller is designed to supply airflow and sealing in synchronization with the cycles of the engine: airflow and fueling supply, sealing, combustion, and re-opening for additional airflow. This controller will supply near-uniform, continuous airflow to the engine. For example, if the pulse detonation engine consists of four combustion chambers, the preferred controller design will duct the inlet diffuser exit airflow to two of the chambers while sealing the other two for the combustion part of the engine operating cycle.
The preferred controller has one or more propeller-like blades that are designed to cyclically and sequentially duct incoming flow to the inlet ports of the combustion chambers, while also providing the capability of sealing the ports during combustion. The blades are aerodynamically designed to provide the desired converging airflow ducting area between the blades from the entrance to the exit to effect proper matching of the airflow from any air intake to a pulse detonation engine. Leading and trailing edges of the blades may be straight or contoured to obtain a desired effective ducting of the airflow. The leading edges are preferably sharp or rounded with a small radius so that the blades effectively present one or more knife edges to the incoming air and the incoming air can flow smoothly, with minimal disruption, past the entire inlet face of the controller. The trailing edges of the blades may also have sharp or curved edges. However, the trailing side of each blade has two edges, separated by a flat surface that seals each port to a combustion chamber as the trailing edge of the blade passes over the port. When the trailing edge of a first blade is aligned with the port to a first combustion chamber, the port will be closed and combustion is initiated within the combustion chamber.
For most applications, the controller will have one blade and one duct for every two combustion chambers in the engine it supplies. As illustrated and described below, for example, with a pulse detonation engine having four combustion chambers (with an inlet port for each chamber) and a flow controller having two blades and two ducts, when the outlet from a first duct is aligned with a first port, the outlet from the second duct will be aligned with port number three, and air or other oxidizing gas can flow into combustion chambers one and three. At the same time, the trailing sealing surfaces of the two blades cover ports two and four, and combustion can be initiated in these chambers. As the controller continues to rotate, e.g. through a 45xc2x0 arc, the outlet from each duct will become partially aligned with two ports, and gas can flow into all four combustion chambers. Further rotation once again brings the outlet from each duct into alignment with one port, leaving the remaining two chamber inlets sealed for combustion. However, as discussed in more detail below, application of this controller is not limited to engines with an even number of combustion chambers. The rotary flow controllers of this invention may have any number of blades and may be used with any number of combustion chambers, even or odd.
This arrangement does not create the flow discontinuities that plagued prior art inlet valves for pulse detonation engines. Airflow through the flow controller is substantially uniform and continuous. The system does not generate large cyclic airflow transients in the air inlet diffuser. As a result, the utilization of the flow controller offers increased efficiency. In the prior art, less than one-half of the available flow area in the entrance duct could be used for airflow ducting at any selected time, allowing only a portion of the available airflow to be processed by the engine. The rotary flow controller allows all of the flow to be processed, thus providing a substantial increase in efficiency. Therefore, a pulse detonation engine in combination with a rotary airflow controller can operate at a much higher combustion frequency because more airflow is available for combustion. The optimum airflow processing by the engine system is important when these engine systems are considered for aircraft propulsion since frontal area imposes a drag penalty. The rotary controller offers the capability of more thrust for a given frontal area of the air intake, or offers the same thrust for an engine with significantly less frontal area, drag, and obviously weight.
The rotary inlet flow controllers of this invention may process flow through all of a circular duct. They may also control airflow through an annular part of a circular duct. This type of controller is particularly suited for a combined engine system, such as a turbojet or turbofan located in the center of a circular duct with a pulse detonation engine located around the periphery to function as an afterburner. Turbojet and pulse detonation engine arrangement of this type can provide the propulsion necessary for flight speeds up to Mach 5. For this engine system, the turbojet/turbofan engine provides thrust for lower-speed conditions up to about Mach 2 to 3, and the pulse detonation engine provides thrust for the higher Mach numbers after the low-speed propulsion engine has been shut down and isolated from temperature effects at high Mach flight conditions. This invention may also be applied to a combined cycle hypersonic propulsion system, with the rotary flow controller and pulse detonation engine located in the center of a circular duct with a combined ramjet and/or scramjet airflow duct positioned in a wrap-around arrangement.
These ducted rotary inlet flow controllers can be used with pulse detonation engines for supersonic, subsonic or hypersonic military or commercial aircraft; with pulse detonation engines for subsonic, supersonic or hypersonic missiles; and with pulse detonation engines for launch vehicles for space access. They can also be used for combustion engines for many other propulsive applications, including rotorcraft, watercraft, or land vehicles. While the preferred use is for flight vehicle propulsion, the rotary airflow controller and pulse detonation engine can be applied as a ground based engine system to produce mechanical work.